InSilc Degradation Module
Compared to permanent BMSs, the design of the next-generation of drug-eluting BVS is complicated by the range of interacting physiochemical parameters that control material degradation in both polymer- and metal-based devices. In the case of synthetic polymers, bulk degradation takes place through a two-phase autocatalytic process, initiated by chemical hydrolysis of the polymer chains, which alters the pH in the local environment, in-turn accelerating the rate of hydrolytic breakdown of the polymer Degradation in metal-based devices generally takes place through an electrochemical process, whereby the alloying elements and an electrolyte form a galvanic cell, which results in heavily localised surface-based pitting corrosion adjacent to the cathode. Capturing the effects of the in vivo environment on bulk- or surface-based degradation mechanisms of polymer and metal-based bioresorbable materials through computational simulation presents significant challenges. The current state-of-the-art in degradation modelling of drug-eluting BVS has largely used phenomenological models to capture material behaviour. In the case of polymer-based degradation, continuum damage mechanics approaches have been developed that capture the effect of polymer chain scission through a degradation damage variable, that operates on materials parameters of the chosen constitutive law. Similarly, metal-based corrosion has been captured through the use of continuum damage mechanics, whereby a corrosion kinetic parameter controls the load-bearing capacity of surface elements.
This module will predict the degradation and long-term mechanical performance of the implanted drug-eluting BVS, using an integrated multiscale and multiphysicspredictive modelling framework.
Already, two deliverables have been completed within this task, describing the progress of the experimental and computational progress in the development of the InSilc Degradation module.
Experimental characterisation of polymer and metallic biodegradable material specimens has been completed. Accelerated in vitro protocols have been used to characterise degradation rates and evolution of mechanical properties on polymer-and metal-based material coupons. Significant progress has been made on the development of the degradation modelling framework for both polymer-and metal-based bioresorbalematerials. It has been demonstrated that these modelling frameworks can capture the degradation behaviour observed experimentally, with predictions compared to accelerated ageing tests. Furthermore, the modelling frameworks under development for the InSilc Degradation Module are demonstrated to be highly flexible and will have the capacity to capture and predict a wide range of device behaviour.